The Center's research has been directed towards strategies for replacement of dopaminergic neurons in the substantia nigra in animal models of Parkinson's disease. Among the strategies developed and evaluated during the previous funding period have been; (1) transplantation of embryonic neurons that have the potential to produce a dopaminergic innervation, (2) infusions of factors that are trophic for dopaminergic neurons, and (3) genetic alteration of cells to make dopamine or growth factors for subsequent transplantation. The central focus of this competing renewal application will be a multidisciplinary study of the recently identified putative dopaminotrophic factor glial cell line-derived neurotrophic factor (GDNF) A second focus of this center will be to further examine properties of transplants of fetal neurons and other types of peripheral cells. This Center will conduct studies of effects of exogenous GDNF on normal mature, aged, lesioned and brain cell-transplanted rodents. In addition, experiments on the roles of endogenous GDNF will be carried out. Experiments to define the biochemical mechanisms of GDNF's trophic activities, in terms of oxidative stress and mitochondrial respiratory enzymes, will also be carried out. Immunological properties of brain cell grafts, and interaction of GDNF with CNS immune mechanisms will be delineated. We will also initiate studies on a second TGF-beta family member, OP-1, which may have a positive effect on dopamine neurons. These studies require an infrastructure of collaborative investigators. First, research strategies must be developed, using the techniques of molecular and developmental biology. Second, the strategies must be evaluated in animal models, using the Center's combined expertise in measuring enzymatic mechanisms, dopamine metabolism and release, neuroanatomical changes, production and transport of mRNA and proteins, electrophysiological change, and normalization of behavioral function after lesion. These studies, which combine brain cell transplantation and trophic factor administration, may ultimately lead to optimal approaches for replacement or preservation of ventral mesencephalic dopamine neurons.